髂骨短钉骨水泥强化与长钉的固定强度比较

目的 评价两种髂骨钉在承受周期性载荷后的固定强度,探讨聚甲基丙烯酸甲酯(poly-met hylmethacrylate,PMMA)强化髂骨短钉固定的生物力学作用.方法 对11具成人尸体标本(男7具、女4具;年龄41～78岁,平均60.7岁)骨盆标本,行双能X线吸收法(DEXA)扫描以确定骨矿物质密度(bone mineral density,BMD),平均值为(0.68±0.17) g/cm2.实验采用配对设计,随机选择一侧髂骨置入直径为7.0 mm、长度为(138±4) mm的髂骨长钉,另一侧置入PMMA强化的直径为7.0 mm、长度为(70±2) mm的髂骨短钉(短钉定义为60～80 mm,长钉定义为100～140 mm), PMMA的注入量为2～5 ml(平均3.6 ml).随后对螺钉施加30～300 N的垂直周期性载荷,载荷频率为2 Hz,加载次数为2000次,最后以5 mm/min的速度进行两种螺钉拔出试验,获得螺钉的最大拔出力.结果 髂骨长钉和髂骨短钉PMMA强化后的初始刚度分别为(249±101) N/mm和(253±122) N/mm.加载周期载荷后,两者的终末刚度分别为(214±92) N/mm和(229±120) N/mm.加载周期载荷后,短钉强化和长钉的最大拔出力分别为(2529±1055)N和(2436±915)N,两者之间差异无统计学意义.两种固定方式的最大拔出力与骨密度呈线性关系.结论 PMMA强化髂骨短钉应用于腰骶骨盆重建是可行的,对于骨质疏松的患者应尽量采用此方法固定.

Biomechanical comparison of long iliac screw and short iliac screw augmenting with PMMA fixa-tions

Objective To compare the strength of long iliac screw and short iliac screw augmenting with PMMA fixations after a fatigue simulation and evaluate the biomechanical effect of the short iliac screw. Methods Eleven adult corpse embalmed pelves (7 males, 4 females, with the average age of 60.7 years, ranged from 41 to 78 years) were used. Using dual energy X-ray absorptiometry (DEXA), bone density was measured to characterize bone quality, the mean value of BMD was 0.68±0.17 g/cm2, long screw was difined as the length of 2 mm around anterior inferior iliac spine, and short screw was difined as the length of exceeding no more than 5ram over ischial notch. Long screw 7.0 mm diameter and (138±4) mm length] was randomly inserted in one side of each pelve, and short screw 7.0 mm diameter and (70±2) mm length] following augmentation with PMMA was inserted in the other side. The PMMA was inserted 2-5 ml (mean 3.6 ml). Cyclic loading from 30 N to 300 N was applied to each screw at a frequency of 2 Hz up to 2000 cy-cles. Pullout tests were conducted at 5 mm/min after completion of the fatigue tests, and the maximum pull-out strength was recorded. Results Initial stiffness of the long screw fixation and the short screw fixation with augmentation were (249±101) N/mm and (253±122) N/mm respectively. Pullout force of the short screw fixation with augmentation and the long screw fixation were (2436±915) N and (2529±1055) N respectively, no significant difference was found between the two groups. The pullout forces of two fixations following cyclic loading showed linear correlations with the bone mineral density of pelvis. Conclusion The short ili-ae screw fixation following augmentation with PMMA will be a viable clinical option for spino-pelvic recon-struction, especially in osteoporotic patients.